Electrode for physiological signal measurements and method for making same

ABSTRACT

Described are an electrode and electrode catheter using thin metallic threads or wires, for example, microwires having diameters as low as 10 −6  to 10 −4  meters or less. The embodiments allow for the efficient mounting of at least one electrode on a catheter, resulting in the creation of a flexible ring-microelectrode that is suitable for, amongst other things, the detection of myoelectrical activity in a patient&#39;s muscle, such as the diaphragm or other inspiratory-related muscle.

FIELD OF THE INVENTION

The present invention relates to an electrode that can be mounted to acatheter, and a catheter including at least one such electrode. Theinvention further includes a method of making the electrode. An assemblyof electrodes in accordance with the present invention is suitable for,amongst other things, detection of myoelectrical activity in a patient'smuscle, such as the diaphragm or other inspiratory-related muscle.

BACKGROUND OF THE INVENTION

Triggering of ventilatory support systems is usually dependent uponrespiratory effort of a patient. Respiratory effort can be detected bymeasuring myoelectrical activity in a respiratory-related muscle of thepatient. A method of measuring such myoelectrical activity is to insertan electrode catheter into the patient's respiratory tract oroesophagus, this electrode catheter being connected to a signalamplifier.

Current manufacturing of electrode catheters typically involves mountingstiff and large contacts that usually come under the form of rings.Those electrodes are commonly mounted directly on the outer surface ofthe catheter. A large contact area is preferred in catheters of whichthe electrodes are used for electrical stimulation. In contrast,however, the measurement of myoelectrical signals, e.g.respiratory-related muscle activity via electrodes located in therespiratory tract, does not require such large surface areas.

Although the use of a ring-shaped electrode is advantageous since thisstructure secures the electrode around the body of the catheter, it haslimitations. Typically, ring electrodes are made from sections of rigidor stiff metal tubing as disclosed for example in U.S. Pat. No.6,588,423 granted to Christer Sinderby on Jul. 8, 2003. This means thatupon insertion of a ring electrode catheter, for example a size-16French nasogastric tube typically of large size relative to the width ofthe passages in which it is inserted (nostrils, throat, oesophagus,etc.), the ring electrodes can damage the mucosa of the nostrils and/orthe upper airways of the patient during both insertion and pulling backof the catheter. In addition to tissue damage, this type of ringelectrode catheters can also cause discomfort to the patient. Therefore,there exists a need in the industry to replace rigid metal ringelectrodes and to develop narrower and/or smoother electrode cathetersthat minimise or eliminate tissue damage caused by both insertion andpulling back of an electrode catheter.

Furthermore, the amount of time and effort involved in manufacturingcatheters is critical to the price of these catheters. Easy andefficient installation of electrode arrays on a catheter would thereforebe of great value.

Last but not least, metals that are approved for the manufacture ofelectrodes used in a human body are limited. Many of these implantmetals are expensive while others are difficult to handle. For example,several types of stainless steel are sanctioned for implantation and canthus be used to make electrodes. However, a great difficulty withstainless steel is that it is very difficult to combine and/or connectwith other metals/materials. Accordingly, attachment of stainless steelwires to a connector is not only costly but can also result in a highlevel of failed connections.

SUMMARY OF THE INVENTION

The present invention proposes an electrode made of a thin metallicthread or wire that overcomes the above discussed drawbacks of theformer electrodes. Such electrodes can be mounted on a catheter todetect myoelectrical activity in a patient's muscle such as, forexample, the diaphragm or other inspiratory-related muscle.

The present invention also proposes a method for making electrodes outof such a thin wire.

More specifically, the present invention concerns a thin-wire, ring-typeelectrode comprising a loop portion and a wire portion. This electrodeis typically made from platinum, gold, titanium, silver, silver chlorideor stainless steel, and has a thickness of about 10⁻⁶ m to 10⁻⁴ m. Inone embodiment, the electrode comprises a protective coating on the thinwire. Such an electrode is suitable for use with a host tube such ascatheter (i.e., an electromyographic (EMG) catheter) or a nasogastrictube.

The present invention further includes a method of making a thin-wire,ring-type electrode as described above, as well a host tube comprisingsuch an electrode, including a catheter or a nasogastric tube. In oneembodiment, the method of making the electrode comprises:

-   -   winding one end of a thin metal wire around a cylinder to form        the loop portion; and    -   fusing the free end of the loop portion of the thin metal wire        to the wire portion.

A number of electrodes may be made in accordance with the invention toproduce an electrode assembly that is suitable for a host tube, such asa catheter. In one embodiment, the method of making such a cathetercomprises:

-   -   winding one end of a thin metal wire around a cylinder to form        the loop portion of the electrode;    -   fusing the free end of the loop portion of the thin metal wire        to the wire portion;    -   mounting the loop portion onto the catheter; and    -   inserting the wire portion into the lumen of the catheter.

The electrode catheter itself is comprised of:

-   -   an elongated tubular body made of resilient material and having        at least one lumen; and    -   an electrode assembly consisting of at least one thin-wire,        ring-type electrode having a loop portion and a wire portion,        wherein the loop portion is positioned around the tubular body        and said wire portion is positioned within the lumen of the        tubular body.

In an alternative embodiment to the present invention, a wire carriermay be used to produce an electrode assembly suitable for positioning ona host tube. This wire carrier comprises:

-   -   at least one transversal indent through which the loop portion        can be mounted on the wire carrier; and    -   a longitudinal, inner groove in which the wire portion of the        electrode can be placed.

Yet another alternative method for making a catheter with a thin-wire,ring-type electrode having a loop portion and a wire portion inaccordance with the present invention comprises:

-   -   inserting a thin-wire electrode bundle that is bent into a        U-shape through an opening in the catheter using a guide wire        having a hook for engaging the loop part of the U-shaped bundle.

The above and other objects, advantages and features of the presentinvention will become more apparent upon reading of the following nonrestrictive description of illustrative embodiments thereof, given byway of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a cross-sectional view of a cylinder and clamp device used tofuse into a loop the end of a thin wire from a spool of this wire;

FIG. 2 is a side view of the cylinder of FIG. 1 with several thin-wirering-type electrodes in a solution to remove the coating from the ringportion of the thin wire;

FIG. 3 is a side view showing a catheter tubing being inserted into thecylinder of FIGS. 1 and 2 provided with several thin-wire ring-typeelectrodes;

FIG. 4 is a side view of a catheter tubing being removed from thecylinder thereby transferring the thin-wire ring-type electrodes ontothe catheter tubing;

FIG. 5 is a side view of a needle inside the wire lumen of a cathetertubing and piercing the wall of the catheter tubing to hook the thinwire forming a ring-type electrode;

FIG. 6 a is a cross-sectional view of a catheter tubing with a wirelumen in which the thin wires forming the ring-type electrodes have beeninserted;

FIG. 6B is a cross-sectional perspective view of a catheter tubing witha wire lumen in which the thin wires forming the ring-type electrodeshave been inserted;

FIG. 7 is a perspective view of elements that make up a connectionbetween a thin-wire ring-type electrode and an amplifier: a hollow boxforming a female connector and a male connector;

FIG. 8 is a side view of a nasogastric tube inserted into a cathetertubing with pre-mounted electrodes;

FIG. 9 is a cross-sectional view of a wire carrier and a host tube;

FIG. 10 is a side view of the indented wire carrier of FIG. 9 with awire loop;

FIG. 11 a is a cross-sectional view of an indented wire carrier with awire loop;

FIG. 11 b is a side view of the indented wire carrier of FIG. 11 a witha wire loop;

FIG. 12 is a cross-sectional view of an indented wire carrier bearing aseries of wire loops, and a host tube; and

FIG. 13 is a cross-sectional perspective view of a host tube with a wirecarrier bearing a series of wire loops.

FIG. 14 is a partial cross-sectional view of a catheter tubing, having aguide wire inserted therein, and an associated cutting tool;

FIG. 15 is a cross-sectional view taken along line II-II of the cuttingtool of FIG. 14;

FIG. 16 is a cross-sectional view taken along line III-III of thecutting tool of FIG. 14;

FIG. 17 is a partial cross-sectional view of the catheter tubing whereina bundle of thin-wire electrodes attached to the wire guide hook isbeing pulled into the catheter tubing as the wire guide distal end isbeing pulled out of the catheter tubing through a cut in the wall of thecatheter tubing;

FIG. 18 is a side view of a bundle of thin-wire electrodes;

FIG. 19 is a partial cross-sectional view of a thin-wire electrodeinside the catheter tubing, the thin-wire electrode having a loopportion exiting the catheter tubing through a cut in the wall of thecatheter tubing;

FIG. 20 is a partial cross-sectional view of a thin-wire electrodeinside the catheter tubing, the thin-wire electrode having a loopportion that is wound around the exterior wall of the catheter tubing;

FIG. 21 is a combination front (FIG. 21 a) and side (FIG. 21 b) views ofa slitted female contact pin;

FIG. 22 is a side view of a thin-wire electrode being wrapped around theslitted female contact pin of FIGS. 21 a and 21 b using a wrapping tool;

FIG. 23 is a combination side (FIG. 23 a) and front (FIG. 23 b) views ofa wrapping tool;

FIG. 24 is a side view of a slitted female contact pin onto which athin-wire electrode has been mounted;

FIG. 25 shows electrical wires (FIG. 25 a) pulled through aprefabricated tube (FIG. 25 b) using a wire guide (FIG. 25 c);

FIG. 26 shows the installation in a catheter of wires grouped in aprefabricated braided tube (FIG. 26 a) with the aid of a guide wire(FIG. 26 b);

FIGS. 27 a and 27 b illustrate a method for producing electrode loopswith the use of a compressing braid;

FIG. 28 illustrates conducting braids made from stainless steel wireswith a cotton core (FIG. 28 a) and without a cotton core (FIG. 28 b);

FIG. 29 illustrates ten Stainless Steel 44A WG wires cut to length andprepared for window strip;

FIG. 30 shows the ten wires of FIG. 29 hooked onto a guide wire to passthe wires through the hollow core of a 0 US silk leaving the windowstrip portion of the wires exposed at the distal end of the silk;

FIG. 31 is a side elevational view showing the wires of FIG. 29 passedthrough the wire lumen from the distal end to the proximal end of aspecially designed polyurethane tube;

FIG. 32 is a side elevational view showing a small puncture in the tubeof FIG. 31 to fish out a single wire and expose the window strip of thiswire to form a small loop;

FIG. 33 is a side elevational view of the tube of FIG. 32 bent to passthrough the loop formed by the wire in turn placing the wire around thetubing; and

FIG. 34 shows the loop tightened snugly around the tube insuring thatthe window stripped portion of the wire is fully exposed on the outsideof the tube.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The non-restrictive illustrative embodiments of the present inventionare concerned with an electrode and electrode catheter using thinmetallic threads or wires, for example, microwires having diameters aslow as 10⁻⁶ to 10⁻⁴ meters or less (there is no known lower limit exceptwith regards to tensile strength of the wire). The embodiments allow forthe efficient mounting of at least one electrode on a catheter,resulting in the creation of a flexible ring-microelectrode that issuitable for, amongst other things, the detection of myoelectricalactivity in a patient's muscle, such as the diaphragm or otherinspiratory-related muscle. Advantageously, and in contrast to oldertechniques, the method of the present invention does not involve a lotof time consuming wire-by-wire pulling.

EXAMPLE 1

According to a first non-restrictive illustrative embodiment, athin-wire ring-type electrode for use with a catheter consists of a loopportion 10 and a wire portion 20. A method for making the loop portion10 and wire portion 20 is illustrated in FIG. 1. A thin wire 30 ofsuitable metal or alloy from a spool 40 is wound around a hollowcylinder 50 to form a loop 10. The free end 60 of the thin wire 30 isclamped by a clamp device 70 to the wire section 20 for fusion. If acoated thin wire is used, both the free end 60 and the wire portion 20can be heated by the clamp device 70, thereby heating and fusing thecoating. An alternate method when using a coated or non-coated thin wireis to apply an extra layer of coating and then letting the coating dry,with or without heat, to fuse the free end 60 to the wire portion 20.Alternative methods for producing the loop portion 10 of the thin wire30 are known and may also be used.

In theory any metal, alloy or conducting material such as conductingpolymers could be chosen as electrode material since the wet environmentof the oesophagus makes the conducting properties less important.However since the electrodes are exposed to the human body the metals,alloys, etc. that can be used are reduced to those that are-nonpoisonous to the human body. Such materials include, in particular butnot exclusively, platinum, gold, titanium, silver, silver chloride andstainless steel as is known to those of ordinary skill in the art.Although stainless steel will be described as a non-limitative examplefor the material of the electrode in the present and following examplesbecause it is strong, non-corrosive and cheap, other materials such asthose indicated in the foregoing description could also be considered aslong as the wires that can be made therewith are sufficiently thin.

Once the free end 60 and the wire portion 20 of the thin wire 30 havebeen fused together, i.e., once the loop 10 of thin wire has beenformed, the wire forming the free end 60 is cut close to the fused areaand sealed. The wire portion 20 is then cut at a desired length.

The process is repeated along the cylinder 50 at desired interspaces andas many times as required to produce a required number of ring-typeelectrodes.

Referring now to FIG. 2, the eventual insulation or coating of the loopportions 10 of thin wire is then removed. A method of removing thecoating consists of dipping the cylinder 50 along with the array 80 ofloop portions 10 in an acid bath or other solvent 90 to dissolve theinsulation or coating of the loop portions 10, thereby leaving the wireportions 20 insulated or coated. In an alternative embodiment, anon-coated thin wire is used to make the loop portions 10 and the wireportions 20, and the wire portions 20 are subsequently coated withelectrical insulation using techniques known to those of ordinary skillin the art.

Referring now to FIG. 3, the loop portions 10 on the hollow cylinder 50are then mounted onto a catheter tubing 100 and preferably on a cathetertubing having a wire lumen 110. The catheter tubing 100 is slid into thecylinder 50 provided with the thin wire loop portions 10, as shown inFIG. 3. To facilitate sliding of the catheter tubing 100 into thecylinder 50 with the thin wire loop portions 10, the catheter tubing 100can be stretched thereby narrowing its diameter. This can be done byfirst introducing a guide (not shown) into the cylinder 50 and attachingit to the distal end 102 of the catheter tubing 100 to pull onto thisdistal end. The loop portions 10 are slid off the hollow cylinder 50 attheir respective positions on the catheter tubing 100 as the hollowcylinder 50 is removed from the catheter tubing 100, as shown in FIG. 4.When the array 80 of loop portions 10 is in the desired position on thecatheter tubing 100, stretching of the catheter tubing 100 is released,thereby expanding its diameter to tightly fit the loop portions 10around the catheter tubing 100 and thereby fixing the array 80 of loopportions 10 in their respective positions. To avoid entanglement of thefree ends of the wire portions 20, the free ends of the wire portions 20can be temporarily attached to a suitable support (see for example 500in FIG. 5) or stored on spools (not shown).

After the operation illustrated in FIG. 4 has been completed, thering-type electrode array 81 (FIG. 5) is in place on the catheter tubing100, but the wire portions 20 must still be inserted or passed throughthe wire lumen 110 of the catheter tubing 100. A method for performingthis operation is illustrated in FIG. 5.

According to the method of FIG. 5, a needle 120 with an eye 121 near thetip 122 is passed through the wire lumen 110 of the catheter tubing 100from a proximal end 101 toward the distal end 102 thereof, through theloop portions 10 until the tip 122 of the needle 120 reaches the mostdistal loop portion 10 ₁. Starting from this most distal loop portion 10₁, the needle tip 122 is pushed to pierce the wall of the cathetertubing 100 until at least a portion (for example, one-half) of the eyeof the needle 121 appears on the outside of the catheter tubing 100,preferably near or at the junction between the loop portion 10 ₁ and thewire portion 20 ₁ of the most distal thin-wire ring-type electrode. Tofacilitate piercing of the wall of the catheter tubing 100 with theneedle tip 122, transversal cuts or holes may be made through thecatheter tubing 100 into the wire lumen 110 prior to this process. Thefree end of the wire portion 20 ₁ is then inserted through the eye ofthe needle 121 and a section of the wire portion 20 ₁ is pulled throughthe eye of the needle 121. The needle 120 is then pulled back away fromthe distal end 102, thereby inserting the wire portion 20 ₁ of the mostdistal thin-wire ring-type electrode 10 ₁, 20 into wire lumen 110 of thecatheter tubing 100.

Then, the needle 120 is pulled back until its tip 122 is located closeto the second most distal thin-wire loop portion 10 ₂ and again theneedle tip 122 is pushed to penetrate the wall of the catheter tubing100 until at least a portion (for example, one-half) of the eye of theneedle 121 appears on the outside of the catheter tubing 100, preferablynear or at the junction between the loop portion 10 ₂ and the wireportion 20 ₂ of the second most distal thin-wire ring-type electrode.The free end 130 of the wire portion 20 ₂ is passed though the eye ofthe needle 121 and the wire portion 20 ₂ is pulled through the eye ofthe needle 121. The needle 120 is then pulled back away from the distalend 102 thereby also inserting the wire portion 20 ₂ into the wire lumen110 of the catheter tubing 100 along with the wire portion 20 ₁ of themost distal thin-wire ring-type electrode.

The above process is repeated for each thin-wire ring-type electrode 10₃,20 ₃ and 10 ₄,20 ₄ of the catheter tubing 100 such as to pull by meansof the needle 121 all the wire portions 20 within the wire lumen 110 ofthe catheter tubing 100, as shown in FIGS. 6 a and 6 b. A method usingseveral needles for simultaneously piercing several point of the wall ofthe catheter tubing 100 to simultaneously pull a plurality of wireportions 20 may also be envisaged without departing from the presentinvention. Also, the number of thin-wire ring-type electrodes 10,20 isnot restricted to four (4).

Once at least a portion of all the wire portions 20 ₁, 20 ₂, 20 ₃ and 20₄ have been pulled into the wire lumen 110 of the catheter tubing 100,the needle 120 is pulled from the wire lumen 110 of the catheter tubing100 such that at least a portion of each of the wire portions 20 ₁, 20₂, 20 ₃ and 20 ₄ protrudes from the proximal end 101 of the wire lumen110. While the wire portions 20 ₁, 20 ₂, 20 ₃ and 20 ₄ are stillinserted in the eye of the needle 120, a shield and/or insulating tubingcan be pushed over the end of the needle 120 opposite to the tip 122.The insulating tubing is pushed past the tip of the needle 122, over thewire portions 20 ₁, 20 ₂, 20 ₃ and 20 ₄ until it reaches the proximalend 101 or a position close to the proximal end 101 of the wire lumen110 of the catheter tubing 100 on which the loop portions 10 ₁, 10 ₂, 10₃ and 10 ₄ are mounted, such as to cover at least a portion of the wireportions 20 ₁, 20 ₂, 20 ₃ and 20 ₄ protruding from the wire lumen 110.The shield and/or insulating tubing is then pushed further into the wirelumen 110 of the catheter tubing 100 and secured to this position suchthat none of the wire portions 20 ₁, 20 ₂, 20 ₃, 20 ₄ are exposed nearthe proximal end 101 of the wire lumen 110.

Then, the loop portions 10 ₁, 10 ₂, 10 ₃ and 10 ₄ on the outside of thecatheter tubing are covered and the holes created in the wall of thecatheter tubing 100 by the needle 120 are filled. This covering and holefilling is performed by dipping the electrode array 82 on the cathetertubing 100 (see FIG. 6 b) in a coating bath or other alternative device(not shown) while ensuring that no dipping material/coating enters thelarge catheter lumen 115 of the catheter tubing 100 that bears the loopportions 10 ₁, 10 ₂, 10 ₃ and 10 ₄.

Referring now to FIG. 8, the electrode array 83 on the catheter tubing100 is mounted or slid on a nasogastric tube 200. To facilitate themounting or sliding of the catheter tubing 100, the nasogastric tube 200can be stretched thereby narrowing its diameter. This can be done byfirst introducing a guide (not shown) in the large catheter lumen 115 ofthe catheter tubing 100 and attaching it to the distal end 201 of thenasogastric tube 200 to pull onto the distal end 201. When the electrodearray 83 is in the desired position, stretching of the nasogastric tube200 is released, thereby expanding its diameter and fixing the electrodearray 83 in this position. For example, to ensure that the electrodearray 83 is fixedly secured in position on the nasogastric tube 200,this nasogastric tube 200 can be coated with glue or similar compound ortreated with a solvent prior to the release of the stretch. Otherfastening or securing methods known to those of ordinary skill in theart may also be used.

The above described method for mounting an electrode array 83 can beeither applied to a separate catheter tubing 100 which is then mountedon a nasogastric tube 200 as shown in FIG. 8, or directly on anasogastric tube whereby the operation illustrated in FIG. 8 is nolonger required.

Use of thin wires, for example microwires having diameters of the orderof 10⁻⁶ to 10⁻⁴ meters, to form a ring around a catheter can efficientlyserve as an electrode to measure signals when surrounded by bodilyfluids or electrolyte charged materials. Also, when fully annealed andcurved, the ring-like thin-wire electrodes are soft and flexible,allowing them to flex or bend with the catheter without damagingsurrounding tissue. Moreover, by using thin wires it is possible to coatthe exterior of the array such that none of the metallic electrodesactually comes into contact with bodily tissues or fluids, therebypermitting the use of a wider variety of metals or alloys to manufacturethe electrodes.

The resulting array of thin-wire ring-type electrodes can be dipped intoa solution to control resistivity between the different pairs oflaterally adjacent electrodes, as taught by International patentapplication No. PCT/CA2004/000550 filed on Apr. 8, 2004. In the samemanner, the resulting array of thin-wire ring-type electrodes can beused in combination with a motion-artifact-reducing interface applied tothe electrodes to prevent direct contact between tissues of the livingbody and the electrodes, as taught by International patent applicationPCT/CA99/00652 filed on Jul. 16, 1999. This applies to all of variousembodiments described below.

In a non-restrictive illustrative embodiment, the hollow cylinder 50shown in FIGS. 1 and 2 can be replaced by a grooved and indented wirecarrier 400, of which examples are illustrated in FIGS. 9, 10, 11 a and11 b. The wire carrier 400 can be of any desired shape and size,examples of which are shown in FIGS. 9, 10, 11 a and 11 b. Wire carrier400 is formed with a series of transversal indents such as 401 atdesired intervals through which the loop portions 10 can be mounted ontothe wire carrier 400 by using, for example, the method shown in FIGS. 1,2 and 3 or any other method of fixing the wire loops onto the wirecarrier 400. The wire carrier 400 also has a longitudinal, inner groove420 in which the wire portions 20 can be placed as shown in FIGS. 10, 11and 12, thereby not necessitating the insertion of the insulated wireportions 20 as illustrated in FIGS. 5, 6 a and 6 b.

After the bared wire loop portions 10 have been mounted on the wirecarrier 400 and after the insulated wire portions 20 have been placedinside the wire carrier 400, the wire carrier 400 can be mounted onto ahost tube 440 (for example a nasogastric tube) with a lumen 460 and agroove 450 adapted to receive the wire carrier 400, as shown, forexample, in FIGS. 9 and 12. The wire carrier 400 is secured in thegroove 450 using mechanical means such as clipping, glue or any othermethod known to those of ordinary skill in the art.

A complete array according to the non-restrictive illustrativeembodiment of FIGS. 9-12 is shown in FIG. 13.

In operation, the thin-wire ring-type electrode array according to theillustrative embodiments of the present invention must be connected to aproper amplifier device. Referring now to FIG. 7, a method of connectingan electrode catheter to an amplifier is shown. Instead of soldering awire to a connector, which can be problematic when using stainlesssteel, for example, and to avoid poor connections due to an intermediateconnector, the proposed method consists of using the wire portions 20 ascontact areas for the electrode array. This method requires no solderequipment. To construct a female connector 300, the insulation is firstremoved from each wire portion 20. Each wire portion such as 20 is woundaround a hollow box 305 made of conductive or non-conductive materialwith openings from the inside out of the hollow box 305, for example,windows 306 to permit direct contact with the wire portion 20 from theinside of the hollow box 305. The wound wire portion 20 is secured onthe hollow box 305 by encapsulating it with glue, plastic or otheradequate coating (not shown). The operation is repeated individually foreach of the other wire portions 20, each wire being wound around aseparate box 305. Each box is then mounted into a main connector body(not shown). The male connector 310 simply comprises spring loaded wiresthat, when inserted into the female connector 300, will contact thewound wire portion 20 of the female connector from the inside of thehollow box 305 through the windows 306. The male connector 310 isconnected directly to an amplifier through a wire such as 320.

Alternatively, the wire portion 20 itself can be used as a connector.For example, the wire portion 20 can be wound onto a spool or otherwiseshaped to form a connector receptacle capable of receiving a malespring-loaded connector plug. In the same manner, the wire portion 20can be wound on a spool or otherwise shaped to form a connector plugcapable of being received into a spring-loaded connector receptacle.

EXAMPLE 2

The following describes an alternative method of making an electrode inaccordance with the present invention.

Turning now to FIG. 14 of the appended drawings, a catheter tubing 700provided with three lumens (only one of which is identified, namelylumen 706). FIG. 14 also shows tools used in the placement of electrodesonto the catheter tubing 700, namely a guide wire 710, which is insertedinto one of the lumens 706, as well as a cutting tool 730 placedadjacent the distal end 701 of the catheter tubing 700. The cathetertubing 700 is advantageously made of resilient material, for exampleplastic material.

According to the non-restrictive illustrative embodiment shown in FIG.14, the guide wire 710 having a hook 712 at its proximal end is insertedinto the lumens 706 at the proximal end 702 of the catheter tubing 700.As better illustrated in FIGS. 15 and 16, the cutting tool 730, which isused to make a controlled opening 740 (see FIG. 17) into the wall of thecatheter tubing 700 near its distal end 701, comprises a razorblade 732with elevated perpendicular knifes 734 ₁, 734 ₂, 734 ₃, 734 ₄, 734 ₅ anda stopper 736 at the top of the knives 734.

Referring to FIGS. 16 and 17, when the cutting tool 730 is applied tothe catheter tubing 700, the razorblade 732 creates a lengthwise slit742 while the knives 734 ₁, 734 ₂, 734 ₃, 734 ₄, 734 ₅ create short rips744 ₁, 744 ₂, 744 ₃, 744 ₄, 744 ₅ radial to the catheter tubing 700. Thestopper 736 defines the depth of the rips 744 ₁, 744 ₂, 744 ₃, 744 ₄,744 ₅ into the wall of the catheter tubing 100. It is to be understoodthat even though five knives 734 ₁, 734 ₂, 734 ₃, 734 ₄, 734 ₅ areshown, any number of knives may be used depending on the application.Optionally, as may be better seen from FIG. 14, the distal end 714 ofthe wire guide 707 may have markings 716 for the positioning of thecutting tool 730 knives 734 ₁, 734 ₂, 734 ₃, 734 ₄, 734 ₅ onto the wallof the catheter tubing 700.

A thin-wire electrode bundle 720 is bent into a U-shape, the loop part726 of which is engaged with the hook 712 of the guide wire 710. Thethin-wire electrode bundle 720, shown in FIG. 18, is composed ofindividual thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ whichare insulated except for each of their respective ends 722 ₁, 722 ₂, 722₃, 722 ₄, 722 ₅ and 724 ₁, 724 ₂, 724 ₃, 724 ₄, 724 ₅. After the opening740 has been created into the wall of the catheter tubing 700 using thecutting tool 730, the guide wire 710 is retracted through the opening740 so that the distal end 714 of the guide wire 710 starts protrudingfrom the lengthwise slit 742. The catheter tube 700 may then bend sothat the guide wire 710 may be pulled through the slit 742, which inturn pulls the loop part 726 of the electrode wire bundle 720 throughthe slit 742 as well.

After the wire guide 710 has exited the catheter tubing 700 through theopening 740, the loop part 726 of the thin-wire electrode bundle 720 isdisengaged from the hook 712 of the wire guide 710. For the sake ofclarity, FIG. 19 illustrates a single thin-wire electrode 720, having aloop part 726 ₁ protruding from the opening 740. The loop part 726 ₁ isthen positioned around the distal end 701 of the catheter tubing 700 andplaced in a corresponding rip 44, (see FIG. 20). By pulling the ends 722₁, 724 ₁ corresponding to the loop 726 ₁ at the proximal end 702 of thecatheter tubing 700, the loop part 726 ₁ is tightened around thecatheter tubing 700. The radial rip 744 ₁ prevents the loop part 726 ₁from being tilted towards the proximal end 702 of the catheter tubing700. The above process is repeated for each of the remaining thin-wireelectrodes 720 ₂, 720 ₃, 720 ₄, 720 ₅.

Once the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ arepositioned within their respective rips 744 ₁, 744 ₂, 744 ₃, 744 ₄, 744₅, the opening 740 may be closed by slightly pulling at the respectiveends 722 ₁, 722 ₂, 722 ₃, 722 ₄, 722 ₅ and 724 ₁, 724 ₂, 724 ₃, 724 ₄,724 ₅ of the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅. Aslight bend of the catheter tubing 700 may help ensure that thethin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ are not stuck inthe opening 740 as its closes. In order not to interfere with alreadypositioned thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅, itmay be advantageous to start positioning the thin-wire electrodes 720 ₁,720 ₂, 720 ₃, 720 ₄, 720 ₅ most towards the proximal end 702 of thecatheter tubing 700. Since all the ends 722 ₁, 722 ₂, 722 ₃, 722 ₄, 722₅ and 724 ₁, 724 ₂, 724 ₃, 724 ₄, 724 ₅ of each of the thin-wireelectrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ are at the proximal end 702of the catheter tubing 700, the risk of having loose electrode endssticking out in the distal end 701 is eliminated.

Use of thin-wires, for example, microwires having diameters of the orderof 10⁻⁶ to 10⁻⁴ meters, to form loops around a catheter may efficientlyserve as electrodes to measure signals when surrounded by bodily fluidsor electrolyte charged materials. Also, when fully annealed and curved,the loop thin-wire electrodes are soft and flexible, allowing them toflex or bend with the catheter without damaging surrounding tissue.Moreover, by using thin-wires it is possible to coat the exterior of thearray such that none of metallic electrodes actually comes into contactwith bodily tissues or fluids, thereby permitting the use of a widervariety of metals or alloys to make the electrodes.

Referring to FIGS. 21, 22, 23 and 24, and with reference back to FIGS.18, 19 and 20, after the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720₄, 720 ₅ have been positioned around the catheter tubing 700, theirrespective ends 722 ₁, 722 ₂, 722 ₃, 722 ₄, 722 ₅ and 724 ₁, 724 ₂, 724₃, 724 ₄, 724 ₅ may be wound around a slitted female or male contact pin755 using a wrapping tool 760 which also releases a spring 752 over thethin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅. The wrappingtool 760 may also be used as an insertion tool for mounting the contactpin 755 in a plastic contact housing (not shown). For the sake ofclarity, only the female version of the contact pin 755 and onethin-wire electrode 720 ₁ are illustrated, though it is to be understoodthat a male contact pin may be used as well and that the procedure holdsfor all remaining thin-wire electrodes 720 ₂, 720 ₃, 720 ₄, 720 ₅.

The wrapping tool 760 keeps the thin-wire electrodes 720 ₁, 720 ₂, 720₃, 720 ₄, 720 ₅ in place as they are wrapped around the contact pin 755.A notch 762 in the spring support 764 of the wrapping tool 760 acts as achannel for the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅.This means that the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720₅ are put through the spring support 764 before the spring 752 ispressed onto the contact pin 755. As the contact pin 755 is spun usingthe rotating pin 766, the spring 752 is pushed away from the springsupport 764 by the spring push-out 768 and lands on the thin-wireelectrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ that are being spun in theopposite direction. When the spinning is finished, constant pressurebetween the thin-wire electrodes 720 ₁, 720 ₂, 720 ₃, 720 ₄, 720 ₅ andthe contact pin 55 is provided by the spring 752.

As a final step, the distal end 701 of the catheter tubing 700 may bedipped in a curing solvent such as, for example, D3 that with capillaryforce fills the lengthwise slit 742 and seals the radial rips 744 ₁, 744₂, 744 ₃, 744 ₄, 744 ₅.

Alternatively, the thin-wire electrode ends 722 ₁, 722 ₂, 722 ₃, 722 ₄,722 ₅ and 724 ₁, 724 ₂, 724 ₃, 724 ₄, 724 ₅ may be used as connectors.For example, the thin-wire electrode ends 722 ₁, 722 ₂, 722 ₃, 722 ₄,722 ₅ and 724 ₁, 724 ₂, 724 ₃, 724 ₄, 724 ₅ may be wound onto a spool orotherwise shaped to form a connector receptacle capable of receiving amale spring-loaded connector plug. In the same manner, the thin-wireelectrode ends 722 ₁, 722 ₂, 722 ₃, 722 ₄, 722 ₅ and 724 ₁, 724 ₂, 724₃, 724 ₄, 724 ₅ may be wound on a spool or otherwise shaped to form aconnector plug capable of being received into a spring-loaded connectorreceptacle. Furthermore, reliable connection to electrical contacts mayalso be improved by using a redundant wire.

EXAMPLE 3

An alternative to the above described embodiments comprises thefollowing mechanical modification in respect of an electromyographic(EMG) catheter.

One of the problems associated with installing a number of isolated verythin (for example, 60 μm thin) stainless steel wires 830 (FIG. 25 a)into a small lumen in the catheter is that it is difficult to keep thewires together, as they tend to get themselves entangled. This problemmakes it difficult to adjust the wires so that just the part that iswithout isolation in on the outside of the catheter.

It has been found practical to collect all wires using a braided tube(not shown) with just a very thin wall which has a low friction to thecatheter and to the isolation on the wires. The use of cable braids inelectrical assemblies is common, preferably as protective cover keepingmultiple cables together. The braid is a woven mesh like tube made ofsynthetic material, and has the property that the diameter of the tubeis reduced if the tube is stretched and vice versa. If the appliedstretching of the tube is removed, the tube will expand to its naturaldiameter as is well known to a person skilled in the art. Braid liketubes of silk are also known from medical applications, sutures, butthese are not as resilient/easily expanded as the synthetic braids. Anovel method to use a braid as an active part in EMG catheter will bedescribed in detail herein below.

The wires can be braided loosely by machine so that the desired wirelength is cut from a spool and the ends are uncovered by removing thebraided tube by heat or other suitable means. Preferably the proximalend 833 has a minor part of the braid uncovered compared to the distalend 834 where the electrode loops are to be formed. The wires are thenreadily isolated. Alternatively, the wires may be pulled through aprefabricated braided tube 880 using a guide wire 810, as illustrated inFIG. 25 b and FIG. 25 c.

To install the wires in the catheter 800, a guide wire 810 with a hookat its distal end is inserted through a hole in a lumen 806 of thecatheter at the proximal end 801 of the catheter as shown schematicallyin FIG. 26 b. When the hook appears in a hole on the distal end 801 ofthe catheter, the hook is inserted into the proximal end 833 of thebraid holding the wire bundle. The braided tube can now be pulledthrough the lumen 806 to the proximal end 802, and the proximal end 834of the braid is pulled out of the lumen 806 at the proximal end 802 orthrough the side of the proximal end 802 of the catheter. Since thebraid itself tends to squeeze the wires as the braid is elongated, thewires are held together by the compression force induced by the hook anda force holding the braid at the distal end 834, there will be less riskof the wires getting entangled within the lumen 806 when pulled throughthe lumen (FIG. 26 a).

Loops are made in the vicinity of the distal end 801. At the proximalend 802, the braided hose runs in a plastic tube for protection to amale connector (not shown).

There are a number of ways to produce said loops without diverting fromthe inventive concept of using a compressing braid. An embodiment isdisclosed in FIGS. 27 a and 27 b. For the sake of clarity only oneunbraided wire is shown. In FIG. 27 a, the wire bundle is in position inthe lumen 806 and the hook is dismantled from the braid, therebylessening the compression force to a minimum. In practice, thecompression force will be close to zero. It is now possible to positionthe individual wire 830 in the lumen 806 by pulling the wire at itsproximal and distal ends 833, 834. The insulation of the wire can bereadily peeled using any suitable method as shown in FIG. 27 a, or thecoating can be removed afterwards as discussed previously in relation toFIG. 2. It is to be noted that only a length corresponding to thecircumference of the catheter is peeled off the wire, thus leaving thedistal end 834 of the wire coated to avoid short circuiting problems.

A piercing needle 884 with a hook can be used to pierce the outer wallof the catheter. The catheter may be marked with a series of dots 883 toindicate the locations of the electrodes, and the needle 884 is pulledout of the catheter having the wire 830 on the hook, as shown in FIG. 27b. A sufficient length of the wire is pulled out of the catheter toposition the loop around the catheter close to the distal end 801, andthe electrode wire loop will position itself when the wire is pulledinto the catheter in a manner similar to what is shown in FIGS. 19 and20. The procedure is repeated for each individual wire 830 to producethe electrodes. The braid can be left inside the catheter or removedprior to the electric connection of the wire at its proximal end 833.

The holes that were made in the catheter during the process of bringingthe braided wire bundle into the catheter to make the electrodes aresealed by any suitable method. Such methods are within the purview ofthose of ordinary skill in the art.

As previously stated, other methods using the braid technique may beused and will be discussed briefly.

A possible method is to follow the procedure disclosed in FIGS. 27 a and27 b but the distal end 834 is peeled completely prior to inserting thewires into the catheter. This simplifies the method used to peel thewire from its insulation, since no chemicals need to be used. In thiscase, the catheter is provided with a small rip at each electrodeposition. This can be done prior to the piercing of the catheter.Instead of bringing out a loop, the entire uncovered distal end 884 isbrought out, wound around the catheter and either fused, tied or knittedin the rip to enhance the positioning of the electrode loop. The holesand rips are sealed, as previously described.

Another method is to provide the braided wires with ready-made loops.For example, the method shown in FIGS. 14 to 20 may be performed inreverse with a braided wire bundle pulled into a slit 42 and each wireloop positioned in a rip 44 defining an electrode position.

EXAMPLE 4

Yet another alternative to the above described embodiments comprises thefollowing electrical modification in respect of an EMG catheter.

In catheters using multiple electrode arrangements for measuring, forexample, EMG signals, a common problem is disturbances caused bytribo-electric charging. This effect occurs in four instances:

-   -   1. Surface contact effects (friction on the molecular level        resulting in chemical bonds that leave imbalanced charges as the        surfaces separate and make contact);    -   2. Work function (material ability to hold onto its free        electrons);    -   3. Charge back flow (two materials that are charged from the        above mechanisms and then separated); and    -   4. Gas breakdown (due to surface topology with microscopic peaks        and valleys, charges on the peaks cause corona discharge moving        charges through the plasma to the other material).

In the embodiments of the present invention, the braided wires have beenpulled through a catheter lumen. The lumen size must therefore beslightly larger than the total diameter of the braided wires because ofthe pulling tool and in order to adjust the wires. When the ready-madecatheter is moved, the wires inside the lumen will scratch against eachother and to the wall of the lumen. Then, the triboelectric charges givea disturbance because of the high impedance in the body contact. Thesemovements in the catheter occur when the catheter is inserted into apatient and the patient moves while breathing, etc. In other words, asmall charge in high impedance of the system can result in a relativelyhigh output voltage, a noise signal. This is a negative effect,particularly if the patient is being treated for a severe condition, anda consequence could be that the equipment connected to the catheterdetects a false pulse and trigger the ventilator in an unwanted way,resulting in a less effective therapy.

To overcome the above problem and minimize the triboelectric effect, thematerial should be carefully selected. Different plastic materialcombinations will have higher triboelectric charges than others.However, by inserting materials that discharge and prevent charges tooccur, the choice of insulators may be made less critically.

An alternative is to introduce conducting materials in the braid. InFIG. 28 a, carbon coal fiber is used in the braid. A positive sideeffect apart from leveling out induced charges is that the braid mayalso be used as a capacitive screen to prevent main disturbances fromreaching the wires. Any conducting or semi-conducting material can beconsidered, such as metals, conducting polymers, etc.

In one embodiment, a stabilizing cotton core is introduced in the wirebundle, as illustrated in FIG. 28 a. The core will keep the thin steelwires in place and evenly distributed around the core. Thus, theinsulation of the wires will be subject to an even distribution ofmovement and a more equal distribution of charges. Cotton is a neutralmaterial that does not cause charges. Dissipating materials may furtherremove charges so that they do not reach the electrodes.

In yet another alternate embodiment shown in FIG. 28 b, a conductingbraid as described above is used. It is similar to the embodiment shownin FIG. 28 a, but differs by not having a cotton core. The electricalproperties will not be as good but will be sufficient. On the otherhand, a smaller lumen can be used, and thus the diameter of the catheterwill be smaller. This may be an important feature to take into accountwhen making catheters intended for infant use.

Furthermore, a possible embodiment is a configuration with a cotton coreas in FIG. 28 a but with the difference in having bare wires withoutinsulation alternating with insulating dummy wires in-between everyconductor to overcome short circuiting problems. This would also requirea braid made of a dissipating material, meaning that the conductivity isless than the conductivity of a semiconductor but better than aninsulator to transport induced charges. The advantage would be that nopeeling of the wires to make the electrode loops are necessary,chemically or mechanically, but the trade off is that twice as manywires has to be configured around the cotton core.

EXAMPLE 5

An additional example is given with reference to FIGS. 29-34. In thisexample, the following operation are conducted:

-   -   1. Referring to FIG. 29, ten Stainless Steel 44A WG wires 900        are cut to length and prepared for window strip (see 901).    -   2. Referring to FIG. 30, the ten wires 900 are hooked onto a        guide wire 902 and passed through the hollow core of a 0 US silk        leaving the window strip portion of the wires exposed at the        distal end of the silk.    -   3. Referring to FIG. 31, the silk 904 containing the wires 900        is hooked to a guide wire and passed through the wire lumen from        the distal end to the proximal end of a specially designed        polyurethane tube 903.    -   4. Referring to FIG. 31, the window strip portion 901 is        positioned 1 cm distal of the ground ring location.    -   5. Referring to FIG. 32, a small puncture 905 is made at the        marked location of the Ground Ring with the sharp tip of a        forcep, a single wire 900 is fished out and the window strip 901        is exposed forming a small loop 906.    -   6. Referring to FIG. 33, the proximal tip 907 of the tube is        carefully passed through the loop 906 formed by the wire in turn        placing the wire around the tubing 903.    -   7. Referring to FIG. 34, both ends of the wire 900 are pulled        until the loop 906 is tightened snugly around the tube 903        insuring that the window stripped portion 901 of the wire is        fully exposed on the outside of the tube 903.    -   8. These above operation 107 are repeated for each remaining        ring.

Although the present invention has been described by way of illustrativeembodiments and examples thereof, it should be noted that it will beapparent to those or ordinary skill in the art that modifications may beapplied to the present particular embodiment without departing from thescope of the present invention.

1. An electrode assembly, comprising: an elongated electrode supportdefining an outer surface, an inner longitudinal conduit, and a wallseparating the outer surface and the inner longitudinal conduit; a wirecomprising a first portion, a second portion, and a third portioninterposed between the first and second portions; wherein the first andsecond portions extend inside the inner longitudinal conduit; whereinthe third portion extends through the wall to form a loop outside theelectrode support and positioned around the outer surface; and whereinthe loop is tightened around the outer surface of the electrode supportby pulling at least one of the first and second portions of the wireextending inside the longitudinal conduit on opposite sides of the loop.2. A method for making an electrode assembly having at least onering-type electrode with a loop portion and a wire portion, comprising:providing an elongated electrode support defining an outer surface, aninner longitudinal conduit, and a wall separating the outer surface andthe inner longitudinal conduit; forming the loop portion of the at leastone ring-type electrode by connecting a first end of a wire to a sectionof said wire spaced apart from the first end, wherein the wire portionof the at least one ring-type electrode comprises the wire between theloop portion and a second end of the wire; encircling the outer surfaceof the electrode support with the loop portion of the at least onering-type electrode, the loop portion then lying on the outer surfacegenerally perpendicular to the elongated electrode support; andinserting the wire portion of the at least one ring-type electrodeinside the inner longitudinal conduit by pulling the second end of thewire within the inner longitudinal conduit across the wall of theelongated electrode support.
 3. A method for making an electrodeassembly as defined in claim 2, wherein forming the loop portioncomprises winding the first end of the wire around a cylinder and fusingthe first end of the wire with said section of the wire to form the loopportion of the at least one ring-type electrode.
 4. A method for makingan electrode assembly as defined in claim 3, comprising repeating theoperations of winding the first end of the wire around the cylinder andfusing the first end of the wire with said section of the wire to formthe loop portion of the at least one ring-type electrode, along thecylinder at desired interspaces to produce a required number ofring-type electrodes.
 5. A method for making an electrode assembly asdefined in claim 3, comprising clamping the first end of the wire beforefusion.
 6. A method for making an electrode assembly as defined in claim3, comprising cutting a free end of the wire close to the fused portionsand sealing the cut free end.
 7. A method for making an electrodeassembly as defined in claim 3, wherein the wire is coated, and whereinthe method further comprises dipping the cylinder in a solvent bath todissolve the coating of the wire in the loop portion.
 8. A method formaking an electrode assembly as defined in claim 3, wherein the cylinderis hollow, the elongated electrode support comprises a catheter tubing,the inner longitudinal conduit comprises a lumen of the catheter tubing,and the method further comprises: repeating the operations of windingthe first end of the wire around the cylinder and fusing the first endof the wire with said section of the wire to form the loop portion ofthe at least one ring-type electrode, along the cylinder at desiredinterspaces to produce a required number of ring-type electrodes;sliding the catheter tubing into the hollow cylinder; and transferringthe loop portions of the ring-type electrodes from the hollow cylinderto the catheter tubing.
 9. A method for making an electrode assemblydefined in claim 2, wherein the elongated electrode support comprises acatheter tubing, and the inner longitudinal conduit comprises a lumen ofthe catheter tubing.
 10. A method for making an electrode assembly asdefined in claim 9, wherein inserting the wire portion of the at leastone ring-type electrode inside the inner longitudinal conduit comprisespiercing the wall of the catheter tubing with a needle and inserting thesecond end of the wire inside the lumen of the catheter tubing using theneedle.
 11. A method for making an electrode assembly as defined inclaim 9, further comprising making at least one opening through the wallof the catheter tubing to facilitate insertion of the wire portion ofthe at least one ring-type electrode.
 12. A method for making anelectrode assembly as defined in claim 11, comprising covering the loopportion of the at least one ring-type electrode on the outer surface ofthe catheter tubing and filling the at least one opening through thewall of the catheter tubing.
 13. A method for making an electrodeassembly as defined in claim 12, wherein covering the loop portion ofthe at least one ring-type electrode on the outer surface of thecatheter tubing and filling the at least one opening through the wall ofthe catheter tubing comprises dipping the loop portion and cathetertubing in a bath of coating material.
 14. A method for making anelectrode assembly as defined in claim 2, wherein the wire is made of amaterial selected from the group consisting of platinum, gold, titanium,silver, silver chloride and stainless steel.
 15. A method for making anelectrode assembly as defined in claim 2, wherein the wire has athickness ranging from about 10⁻⁶ m to about 10⁻⁴ m.
 16. A method formaking an electrode assembly as defined in claim 2, wherein the at leastone ring-type electrode comprises a series of ring-type electrodes, andwherein the method comprises dipping the loop portions of the ring-typeelectrodes into a solution to control resistivity between successivepairs of laterally adjacent ring-type electrodes of the series.
 17. Amethod for making an electrode assembly as defined in claim 2,comprising applying a motion-artifact-reducing interface to the loopportion of the at least one ring-type electrode to prevent directcontact between tissues of a living body and the loop portion of the atleast one ring-type electrode.
 18. A method for providing a catheterwith thin-wire, ring-type electrodes each having a loop portion and awire portion, comprising: producing an opening in the catheter;inserting a guide wire with a hook through the opening in the catheter;bending a bundle of thin-wire, ring-type electrodes into a U-shape;engaging the U-shaped-bent bundle of electrodes with the hook of theguide wire; and p1 inserting the U-shaped-bent bundle of electrodesthrough the opening in the catheter using the guide wire of which thehook engages the U-shaped-bent bundle of electrodes.
 19. A method asdefined in claim 18, wherein the wire of the electrodes is made frommaterial selected from the group consisting of: platinum, gold,titanium, silver, silver chloride and stainless steel.
 20. A method asdefined in claim 18, wherein the wire of the electrodes has a thicknessranging from about 10⁻⁶ m to about 10⁻⁴ m.
 21. A method for making anelectrode assembly having at least one ring-type electrode, comprising:providing an elongated electrode support defining an outer surface, aninner longitudinal conduit, and a wall separating the outer surface andthe inner longitudinal conduit; inserting a wire inside the innerlongitudinal conduit; pulling out a first portion of the wire throughthe wall to form a loop outside the electrode support, the first portionbeing interposed between second and third portions of the wire;positioning the loop around the outer surface of the electrode support;and tightening the loop around the outer surface of the electrodesupport by pulling at least one of the second and third portions of thewire left in the longitudinal conduit on opposite sides of the loop. 22.A method for making an electrode assembly as defined in claim 21,wherein pulling out the first portion of the wire through the wallcomprises hooking the first portion of the wire.